Extruded nut formation

ABSTRACT

A method of forming a sheet metal part including a nut structure by providing a sheet of metal, forming a tubular structure projecting integrally from the main body of the sheet, and tapping the tubular structure to form an internal screw thread within the tubular structure. The method is carried out on a press having a plurality of spaced stations including a punch station and a working station. The tubular structure is formed by punching a hole in the sheet at the punch station and thereafter forming the tubular structure in surrounding relation to the hole in a single hit of the press at the working station. The hole is punched in the sheet utilizing a punch and die wherein the diameter of the die is no greater than approximately five percent greater than the diameter of the punch whereby to provide a hole having a cleanly cut sidewall and thereby preclude splitting of the metal of the sheet as the tubular structure is formed at the working station. A coin formation is also formed in the single hit of the press at the working station to accommodate the head of an associated threaded plug adapted to be threaded into the internally threaded tubular structure.

FIELD OF THE INVENTION

[0001] This invention relates to sheet metal forming and more particularly to a method of forming a sheet metal part having an extruded nut formation.

[0002] Stamped sheet metal parts are widely used in industry including, for example, the automotive industry. It is often required to provide a nut structure in association with a sheet metal part to enable the sheet metal part to receive a threaded member. Common practice is to provide the nut structure on the sheet metal part by punching a hole in the part and thereafter welding a nut to the part in surrounding relation to the hole. While this arrangement is effective in providing the desired nut structure on the sheet metal part, it is expensive in the sense that it requires a separate nut, requires expensive welding equipment to weld the nut to the sheet metal and in general is very labor intensive. This arrangement is also subject to weld failure. In an attempt to overcome the problems with the welded nut arrangement, attempts have been made to extrude a nut formation directly out of the material of the sheet metal. Whereas these extrusion attempts have been generally successful in providing a satisfactory nut structure, the procedure has required a series of hits or strikes on the sheet metal to form the tubular structure of the nut. This series of hits is time consuming and requires very large and very expensive stamping equipment.

SUMMARY OF THE INVENTION

[0003] This invention is directed to an improved method of forming a nut structure on a sheet metal part.

[0004] The invention relates to a method of forming a sheet metal part including a nut structure by providing a sheet of metal, forming a tubular structure projecting integrally from the main body of the sheet, and tapping the tubular structure to form an internal screw thread within the tubular structure.

[0005] According to the invention, the method is carried out on a press having a plurality of spaced stations including a punch station and a working station, and the tubular structure is formed by punching a hole in the sheet at the punch station and thereafter forming the tubular structure in surrounding relation to the hole in a single hit of the press at the working station. This methodology allows minimization of the press equipment required to form the tubular structure and further allows minimization of the time required to form the tubular structure.

[0006] According to a further feature of the invention, the hole is punched in the sheet utilizing a punch and die wherein the diameter of the die is no greater than approximately five percent greater than the diameter of the punch whereby to provide a hole having a cleanly cut sidewall. This methodology minimizes stress in the sidewall of the punched holes and thereby precludes splitting of the metal of the sheet as the tubular structure is formed at the working station.

[0007] According to a further feature of the invention, the formation of the tubular structure at the working station comprises an extrusion step. The provision of a clean unstressed hole allows the tubular structure to be formed in a single continuous extrusion of the sheet metal in a single hit at the working station.

[0008] According to a further feature of the invention, the method includes the further step of forming a coin formation at the juncture of the tubular structure and the planar main body of the sheet, and the formation of the coin formation is performed in the single hit of the press at the working station. This arrangement allows the resulting sheet metal part to be utilized in association with a plug having a threaded main body and an enlarged head, the threaded main body of the plug being threadably received in the threaded tubular structure and the head of the plug being seated in the coin formation.

[0009] The invention also provides a method of forming a sheet metal part including a nut structure adapted to receive a plug having a threaded main body and an enlarged head. According to the invention, a sheet of metal is provided; the sheet is worked to form a tubular structure projecting integrally from the planar main body of the sheet and a coin formation at the juncture of the tubular structure with the planar main body of the sheet having a diameter sized to receive the head portion of the plug; and the tubular structure is tapped to form an internal screw thread within the tubular structure. With this arrangement, the threaded main body of the plug may be threadably received in the threaded tubular structure and the head of the plug may seated in the coin formation.

[0010] Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:

[0012]FIG. 1 is a schematic view of a stamping press for carrying out the methodology of the invention;

[0013]FIG. 2 is a perspective view of a differential cover which may be formed utilizing the invention methodology;

[0014]FIG. 3 is a cross sectional view taken on line 3-3 of FIG. 2;

[0015]FIGS. 4 and 5 are detail views showing a punching step carried out at a punch station on the press;

[0016] FIGS. 6-12 are successive views showing the formation of a tubular structure and a coin formation at a working station on the press;

[0017]FIGS. 13 and 14 are detail views of a form punch utilized at the working station;

[0018]FIGS. 15 and 16 are detail views of a lower form button utilized at the working station;

[0019]FIGS. 17 and 18 are detail views of a button insert or anvil utilized at the work station;

[0020]FIG. 19 is a perspective view of a plug assembly for use with the differential cover of FIGS. 2 and 3;

[0021]FIG. 20 is a detail view taken within the circle 20 of FIG. 3; and

[0022]FIG. 21 is a detail view of a prior art weld nut structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0023] The invention is described with respect to the formation of a automotive differential cover 10 seen in perspective in FIG. 2 and in cross section in FIG. 3. Cover 10 is formed in a stamping operation of a suitable sheet metal material and, in known manner, includes a peripheral lip portion 10 a including holes 10 b to facilitate attachment of the cover to the main body of the differential; a dished central main body portion 10 c including a platform portion 10 d; and a threaded tubular structure 10 e projecting upwardly (as viewed in FIGS. 2 and 3) into the hollow of the dished formation of the cover. This invention concerns the manner in which the threaded tubular structure 10 e is formed in the cover as well as the manner in which the tubular structure is formed to accommodate the enlarged head portion 12 a of an associated drain plug 12 (FIG. 19) having a threaded main body portion 12 b adapted to be threadably received in the threaded tubular portion 10 e of the cover.

[0024] The methodology of the invention is carried out utilizing a stamping press 14 (seen schematically in FIG. 1) of generally known configuration and operation and including a ram 16 and a bed 18 positioned beneath the ram. The ram 16 is arranged to move up and down with respect to the bed 18 in known manner utilizing guide rods 20 so as to cooperate with dies positioned at successive stations along the bed to perform successive cutting and forming operations with respect to a sheet S of sheet metal as the sheet is moved successively incrementally along the bed in known manner.

[0025] Moving successively along the bed from right to left as viewed in FIG. 1, the bed includes successive dishing stations D1, D2, and D3; a punch station P; a working station W; a tapping station T; and a die cutting station DC. It will be understood that the sheet is moved continuously and incrementally along the bed so as to pause at each workstation. It will be further understood that at each pause at a respective workstation, the ram is moved downwardly allowing forming dies carried by the ram to coact in known manner with lower dies positioned on the bed at the respective workstation to perform a forming operation on the sheet.

[0026] In broad overview, as the sheet S moves along the bed 26 between successive stations, upper forming dies 22, 24, and 26, carried by the ram 16, coact with lower dies positioned respectively at stations D1, D2, and D3 to successively form the sheet and, specifically, to form the flange portion 10 a of the differential cover and the dished main body portion 10 c of the cover, including the platform portion 10 d. The sheet is then moved to the punch station P where a piercing punch 28 coacts with a lower die positioned at the punch station P to punch a hole 30 in the platform portion 10 d of the cover, whereafter the cover is moved to the working station W where a forming punch 32 coacts with suitable lower dies at the working station to form the tubular structure 10 e projecting downwardly (as viewed in FIG. 1) from the platform section 10 d. The cover is then moved to the tapping station T where a suitable tap 34 carried by the ram operates to form an internal screw thread 10 f within the tubular structure 10 e whereafter the cover is moved to the die cut station DC where an upper cutting die 34 carried by the ram coacts with a suitable lower cutting die carried by the bed to sever the cover from the balance of the sheet and allow the separated cover to fall downwardly into a part bin 36 whereafter the scrappage may be suitably disposed of and/or recycled.

[0027] The successive dishing operations carried out at stations D1, D2, and D3 (and whatever further stations may be required) are known and do not form a part of this invention. This invention concerns primarily the punching operation carried out at station P and the working operation carried out at station W.

[0028] The punching operation carried out at station P is best seen in FIGS. 4 and 5. As seen in FIG. 4, a bolster or pad 38 is urged downwardly by nitrogen cylinders 39 to clamp the sheet S against bed 18 at the punching station P, whereafter punch 28 is moved downwardly by the ram 16 and coacts with a lower die 40 positioned in the bed 18 to punch a hole 42 in the sheet. It is critical to the successful carrying out of the invention methodology that the cylindrical sidewall 42 a of the hole 42 have a substantially smooth, sheared surfaced for the majority of the depth of the hole. In this regard it is critical that the majority of the depth of the hole be formed by shearing or cutting coaction between the punch 28 and the die 40 rather than by breakage of the slug of the sheet out of the hole with resultant broken or rough surface formations in the sidewall of the hole.

[0029] It has been found that the areas of a punched hole where the slug has broken out of the hole, rather than being cut out of the hole, are areas of high stress concentration which limit the ability of the sheet metal in surrounding relation to the hole to be shaped or formed in subsequent operations. More specifically, It has been found that maximizing the depth of the cleanly cut area of the hole sidewall maximizes the ability of subsequent devices on the press to perform subsequent extrusion operations on the sheet and it has further been found that minimizing the difference between the diameter of the punch and the diameter of the coacting lower die has the effect of maximizing the cleanly cut depth of the hole. Even more specifically, it has been found that the use of a lower die having a diameter no greater than approximately five percent greater than the diameter of the punch provides a hole having a cleanly cut sidewall and a hole in which stress concentrations are minimized.

[0030] As illustrated in FIG. 5, the use of a lower die having a diameter no greater than approximately five percent more than the diameter of the punch produces a hole sidewall 42 a having a cleanly cut depth 42 b that is at least seventy percent of the total depth of the hole leaving a breakage area 42 c that is no more than thirty percent of the depth of the hole, whereby to minimize stress concentrations in the sheet metal around the hole. Specifically, the minimization of stress in the hole 42 a resulting from the use of a lower die having a diameter no greater than approximately five percent greater than the diameter of the associated punch allows the tubular structure 10 e to be formed in the cover at the working station W in a single strike or hit of the press without generating any splits in the sidewall of the tubular structure 10 e so that the tubular structure may successfully accommodate the subsequent tapping operation at the tapping station T.

[0031] The forming operations carried out at the working station W are carried out utilizing upper forming punch 32 acting in coaction with a lower form button 44 carried by bed 18 and a button insert or anvil 46 positioned within lower form button 44 and seated at its lower end 46 a on the piston 50 of a nitrogen cylinder 52 positioned in the bed in underlying relation to button insert 46. In overview, and as shown in successive FIGS. 8-12, upper form punch 32 coacts with lower form button 44 and button insert 46 at working station W to form the tubular section 10 e, as well as a coin formation 10 g at the juncture of the tubular structure with the planar main body of the sheet, in a single strike or hit of the press at the working station.

[0032] Upper form punch 32 (FIGS. 13 and 14) includes an upper main body portion 32 a; an extruding portion 32 b having a generally cylindrical configuration; a forming portion 32 c having a spherical segment configuration; a guide portion 32 d, including an upper cylindrical section 32 e and a lower rounded pilot section 32 f; and a coining shoulder 32 g defined at the juncture of main body portion 32 a and extruding portion 32 b.

[0033] Lower form button 44 (FIGS. 15 and 16) has a tubular configuration including an outer periphery 44 a sized to fit in a socket 18 a in bed 18; a central bore 44 b; and a counterbore 44 c proximate the upper face 44 d of the button.

[0034] Button insert or anvil 46 (FIGS. 17 and 18) includes a cylindrical lower end portion 46 a seated on the piston 50 of nitrogen cylinder 52, and a cylindrical main body portion 46 b upstanding from lower end 46 a and defining an outer periphery 46 c sized to fit slidably within the bore 44 b of lower form button 44 and an upper blind central bore 46 d opening in the upper face 46 e of the insert and sized to slidably receive the guide portion 32 d of upper form punch 32.

[0035] In FIG. 6, the parts are shown as the sheet S arrives at working station W and is halted at the working station with the previously punched hole 42 a aligned with the central bore 46 d of button insert 46. Punched hole 42 a preferably has a diameter substantially corresponding to the diameter of bore 46 d so that bore 46 d with the sheet halted at the working station, forms a flush downward continuation of the sidewall 42 a of hole 42.

[0036] In FIG. 7, the upper form punch 32 has been moved downwardly by the ram to position the guide portion 32 d in bore 46 d and position form portion 32 c against the upper face of the sheet proximate hole 42.

[0037] In FIG. 8, form punch 32 has moved further downwardly to engage the form portion 32 c with the upper face of the sheet around hole 42 and flare the portion of the sheet around the hole downwardly with the downward flaring of the sheet permitted by downward movement of button 46 against the resistance of nitrogen cylinder 52.

[0038] In FIG. 9, the downward movement of button 46 has continued to allow further downward movement of the upper form punch whereby to begin to extrude the sheet material surrounding the hole downwardly between the inner bore 44 b of lower form button 44 and the forming portion 32 c of the upper form punch 32. Button insert 46 continues to move downwardly within lower form button 44 against the resistance of the collapsing nitrogen cylinder 52.

[0039] In FIG. 10, the downward movement of the upper form punch 32 has continued as permitted by further downward movement of button insert 46 against the collapsing resistance of nitrogen spring 52 to extrude the sheet material around the hole between the cylindrical surface of extruding portion 32 b and bore 44 b.

[0040] In FIG. 11, upper form punch 32 has continued to move downwardly as permitted by the continued downward movement of button 46 against the collapsing resistance of nitrogen spring 52 to continue the extrusion of the sheet metal around section 32 b and to allow the formation of a coin formation 10 g at the juncture of the tubular structure 10 e with the planar main body of the sheet. Coin formation 10 g is defined by the coaction of the coining shoulder 32 g of the upper form punch with the counterbore 44 c in the upper face 44 d of the lower form button.

[0041] In FIG. 12, and following completion of the extrusion operation as seen in FIG. 11, the ram is raised to remove the upper form punch from the sheet, lift the bolster from the sheet and allow the sheet to be incremently moved in known manner to bring the extruded tubular section 10 e into alignment with tap 33 whereafter the press is again lowered in known manner and the tap is positioned within the tubular structure and rotated to form an internal screw thread 10 f within the tubular structure whereafter the ram is again raised to allow the sheet to be moved incrementally to the die cut station DC where the ram is again lowered to allow the die 34 to act in coaction with a lower die to sever the differential cover from the sheet and allow the cover to drop downwardly into parts bin 36.

[0042] Whereas the dimensions and configurations of the various parts will vary depending upon the particular application, successful results have been obtained using two millimeter sheet metal stock and using parts having the following dimensions:

[0043] punch 28, diameter Y=0.375 inches;

[0044] die 40, internal bore diameter X=0.385 inches;

[0045] upper form punch 32;

[0046] main body 32 a diameter=1.25 inches and length=4 inches;

[0047] extruding portion 32 b diameter=0.725 inches and length =0.425 inches;

[0048] form portion 32 c radius=0.250 inches and height=0.260 inches;

[0049] cylindrical section 32 e diameter=0.373 inches and height=0.19 inches;

[0050] pilot section 32 f radius=0.5 inches and height=0.335 inches;

[0051] lower form button 44, outside diameter=1.750 inches, internal diameter=0.830 inches, counterbore 44 c =1.320 inches, height=1.5 inches, and depth of counterbore 44 c=0.075 inches;

[0052] button insert 46, outside diameter=1.0 inches, height=1.75 inches, diameter of bore 46 a=0.375 inches, depth of bore 46 d=1.13 inches.

[0053] The tubular sidewall of the tubular structure 10 e formed using parts dimensioned in accordance with the above had a thickness of 1.50 millimeters, as opposed to the starting thickness of the sheet of two millimeters, and the coin formation 10 g had a wall thickness of 1.75 millimeters. It has been found that, using parts dimensioned in accordance with the above, it was possible to form the tubular section 10 e at the working station in a single stroke or hit of the press without producing any cracks in the wall of the tubular structure. It is believed that this ability to extrude the tubular section in a single strike, as opposed to prior art efforts requiring a multiplicity of gradual strikes to avoid splitting, is due, at least in part, to carefully controlling the punching operation at the punch station, and, specifically, insuring that the diameter of the lower die is no greater than approximately five percent greater than the diameter of the upper punch, whereby to provide a hole having a substantially cleanly cut sidewall with a minimum of sidewall breakage and thereby a minimum of stress in the material surrounding the hole.

[0054] The invention will be seen to enable the formation in the single strike of the press of both a tubular structure projecting integrally from the planar main body of the sheet and a coin formation, at the juncture of the tubular structure with the planar main body of the sheet, having a diameter sized to receive the head portion of a plug such as the drain plug seen in FIG. 19.

[0055] Specifically, the threaded main body 12 b of the plug 12 is configured to coact with the internal thread 10 f of the tubular section 10 e and both the head 12 a of the plug and a plastic gasket 54 forming a part of the plug assembly may be seated in the coin formation 10 g. For example, with the dimensions previously specified, the coin formation would define an internal diameter of approximate 1.190 inches and the head of the plug 12 a and the gasket 54 would be dimensioned to fit snugly within that dimension. The positioning of the plug in the tubular section, including the seating of the plug head 12 a and the gasket 54 in the coin formation 10 g, is best seen in FIG. 20. By comparison, the prior art methodology is shown in FIG. 21 wherein a separate nut 56 is welded at 58 to the sheet S in surrounding relation to the previously punched hole in the sheet with the gasket 54 positioned against the outer face of the sheet and the head positioned in turn against the gasket.

[0056] As previously noted, this prior art methodology requires the expense of providing a separate nut 56, including inventorying the nut; requires the capital expense of providing expensive welding equipment to form the weld 58; is subject to the possibility of weld failure; and is labor intensive. Further, it will be seen that the leakage path provided by the invention methodology as seen in FIG. 20 is much more convoluted than the leakage path provided by the methodology seen in FIG. 21, thereby providing a better seal for the differential lubricant contained within the associated differential case.

[0057] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law. 

What is claimed is:
 1. In a method of forming a sheet metal part including a nut structure by providing a sheet of metal, forming a tubular structure projecting integrally from the main body of the sheet, and tapping the tubular structure to form an internal screw thread within the tubular structure, the improvement wherein: the method is carried out on a press having a plurality of spaced stations including a punch station and a working station; and the tubular structure is formed by punching a hole in the sheet at the punch station and thereafter forming the tubular structure in surrounding relation to the hole in a single hit of the press at the working station.
 2. A method according to claim 1 wherein: the hole is punched in the sheet utilizing a punch and die wherein the diameter of the die is no greater than approximately five percent greater than the diameter of the punch whereby to provide a hole having a cleanly cut sidewall and thereby preclude splitting of the metal of the sheet as the tubular structure is formed at the working station.
 3. A method according to claim 2 wherein the formation of the tubular structure at the working station comprises an extrusion step.
 4. A method according to claim 3 wherein: the method includes the further step of forming a coin formation at the juncture of the tubular structure and the planar main body of the sheet; and the formation of the coin formation is performed in the single hit of the press at the working station.
 5. A method of forming a sheet metal part including a nut structure adapted to receive a plug having a threaded main body and an enlarged head, the method comprising: providing a sheet of metal; working the sheet to form a tubular structure projecting integrally from the planar main body of the sheet and a coin formation at the juncture of the tubular structure with the planar main body of the sheet having a diameter sized to receive the head portion of the plug; and tapping the tubular structure to form an internal screw thread within the tubular structure, whereby the threaded main body of the plug may be threadably received in the threaded tubular structure and the head of the plug may be seated in the coin formation.
 6. A method according to claim 5 wherein the working step includes an extrusion step wherein metal of the sheet is extruded into a die to form the tubular structure.
 7. A method according to claim 6, wherein, prior to the working step, a hole is punched in the sheet whereafter the working step is performed in concentric relation to the hole.
 8. A method according to claim 7 wherein: the hole is punched in the sheet utilizing a punch and die wherein the diameter of the die is no greater than approximately five percent greater than the diameter of the punch whereby to provide a hole having a cleanly cut sidewall and thereby preclude splitting of the metal of the sheet as the tubular structure is extruded at the working station.
 9. A method according to claim 8 wherein: the method is carried out on a press having a plurality of spaced stations including a punch station where the punching operation is performed and a working station where the working step is performed; and the tubular structure is formed in a single hit of the press at the working station.
 10. A method according to claim 9 wherein the coin formation is also formed in the single hit of the press at the working station.
 11. A method according to claim 10 wherein: the sheet has a starting thickness; and the tubular structure has a thickness less than the starting thickness of the sheet.
 12. A method according to claim 11 wherein the method further includes forming the planar main body of the sheet into a contoured structure in surrounding relation to the tubular structure.
 13. A method according to claim 12 wherein: the contoured structure comprises a dish; and the tubular structure is formed proximate the bottom of the dish and projects upwardly into the hollow of the dish.
 14. A method according to claim 11 wherein the method includes: moving the sheet along a linear feed path to bring a first section of the sheet into alignment with the working station; performing the working step on the first sheet section at the working station to form the tubular structure and the coin formation on the first section; and thereafter moving the sheet along the feed path to bring successive sections on the sheet into alignment with the working station to allow the working step to be successively performed on the successive sections to form successive tubular structures and coin formations on the successive sections.
 15. A method according to claim 14 wherein: a tapping station is provided along the feed path downstream of the working station; and each successive sheet section, following formation of the tubular structure and coin formation at the working station, is moved along the feed path to the tapping station where the tapping step is performed to provide internal screw threads on the respective tubular structure.
 16. A method according to claim 15 wherein a punching station is provided along the feed path upstream of the working station; and each successive sheet section, upon arrival at the punch station, is punched to form a hole in the sheet section whereafter the section is moved to the working station where the tubular structure and coin formation are formed in concentric relation to the respective hole. 